The invention relates to electric motors in general and, in particular, to direct current motors which can be configured as either inner rotor motors or outer rotor motors. Even more specifically, the motor could be an electronically commutated, brushless DC motor or any other permanent magnet motor. Such motors include a rotor assembly which is connected to a shaft and has one or more permanent magnets, as well as a stator assembly which includes a stator, composed, for example, of laminations, and phase windings. Two bearings are arranged on the shaft at an axial distance from each other in order to support the rotor assembly relative to the stator assembly. As a rule, such motors also have a sensor device to register the rotational position, the rpm and/or the torque of the rotor assembly relative to the stator assembly. The sensor device can, for example, include a position sensor.
The electric motor presented in the invention is particularly intended for application in the automobile sector, for example, to support the steering, to drive a cooling water pump arranged separately from the engine of a vehicle or as a gear shift motor. Such motors frequently find application in the internal-combustion engine compartment of a vehicle where they are subjected to high temperatures and extreme temperature changes. Particularly in all-terrain vehicles which make special demands on the motor such as its fording ability (ability to be immersed in water), the changes in temperature to which the electric motor is subjected can be very high. At the same time, care has to be taken that no water or any other type of pollutant can penetrate into the motor. This means that these motors have to be protected against such outside influences and be of a robust construction, and at the same time they have to be able to withstand extreme changes in temperature.
An electric motor with a fully closed design is known from DE 36 35 297 which is cooled by a fluid circulating in the closed housing, whereby pressure equalizing devices are provided in the motor to equalize the volume or pressure of the coolant.
An electric motor is known from DE 44 44 643 in which a pressure equalizing device takes the form of a PTFE membrane which is arranged in a connecting channel between the interior of the electric motor and the outside air. The pressure is equalized by an exchange of air, whereby the membrane prevents moisture from penetrating into the interior of the motor housing.
One object of the invention is to provide a motor housing for an electric motor which guarantees optimal functionality of the motor even during extreme changes in temperature.